Ground-based users of ground-based wireless networks may expect a near 100% level of interference free connectivity to the wireless network. While such interference free connectivity may have become the norm rather than the exception, tolerance for interference to this near 100% level of ground-based connectivity may have decreased to near zero among users and customers.
Potential airborne users connected to the ground-based wireless network may experience challenges to connectivity. Interference with a second airborne user connected to the ground-based wireless network may cause disrupted connectivity, incomplete connectivity, and possibly an inability to connect.
Ground-based cellular networks are nearly ubiquitous throughout many geographic areas. Build out of wireless networks continues and may be near 100% in many areas. Various worldwide network connectivity technologies may be available including code division multiple access (CDMA), global system for mobile (GSM), universal mobile telecommunications system (UMTS), and long term evolution (LTE). Such ground-based wireless networks may possess more time/spectrum availability than may presently be in use by ground-based users. Specifically, more recent advancements in network connectivity technology may enable current networks to increase time/spectrum availability throughput of each network.
Demand for airborne connectivity to a ground based network has increased. Increased use of network access by airborne users may increase productivity during previously unproductive airborne periods. Airborne users may account for an increasing number of access points to ground based networks.
An airborne user desiring connectivity to a ground-based network may have a limited number of options from which to choose to connect to the ground-based network. For example, satellite based wireless networks may be available to an airborne user to connect via a two-way signal transmitted from earth to satellite to aircraft. Similarly, two-way air-to-ground RF connectivity may be available allowing data connectivity between an airborne user and a ground network via an RF signal transmitted to dedicated RF networks.
On occasion, these airborne users may experience a lack of connectivity to satellite based signals and current ground based signals. This lack of connectivity may stem from a variety of sources, some of which may include a distance between a user and the receiving antenna, bandwidth limitations inherent in the existing connectivity scheme, and an incorrect antenna look angle. This lack of connectivity may decrease value of network connectivity methods as well as reduce connectivity options for airborne users.
During air-to-ground RF transmissions, an aircraft radio may be at an advantaged position as compared to a ground based radio. With equal power, a transmission pattern of the aircraft antenna may cover a larger geographical area than the transmission pattern of a provider's ground-based antenna. Potential interference may occur between airborne users and ground users connecting in the same RF frequency band with the same tower of the wireless network. While reuse of cellular ground towers is an attractive idea for air-to-ground concepts, it may be difficult to pin-point the beam of an airborne antenna to a small geographical location to transmit to a small set of towers for the uplink (i.e. the transmission from user to tower). Longer wavelengths in the 700 MHz cellular bands may prevent development of air antennas with a resolution of less than 18 degrees in azimuth. This small angle however may enable dozens of ground-based towers to be illuminated when the airborne antenna is pointed near the horizon.
Similarly, an airborne radio maintains challenges in connecting to the plurality of towers of the ground-based wireless network. The airborne radio maintains line of sight connectivity potential to a plurality of connection nodes (towers) of the ground based wireless network. Maintaining a connection to one tower may be impossible since the air vehicle upon which the airborne radio may be mounted may be free from physical obstructions found when using a ground-based radio. Additionally, the speed with which the aircraft may travel may require a roaming capability between not only additional towers of the wireless network but also separate carriers owning and managing the towers of the wireless network.
While it may be technically possible to operate an air-to-ground link with this issue, even a small amount of interference may exceed the tolerance of current ground network managers and users. Any increase in interference may be unacceptable, resulting in an inability to make calls, lost calls, and lower data rates for the ground-based users. This antenna beam geometry challenge (beam size and pointing sensitivity) may not be practically controllable at greater ranges. Short-range beam pointing may help limit the number of towers “visible” to the airborne antenna. However longer ranges required in areas with greater spacing between towers (i.e. in mountainous and less populated areas where towers may be more than 100 miles apart), may cause significant problems. At 10,000 feet altitude, with a near horizontal antenna look angle, airborne antenna with a fixed lateral beam width at a range of 130 miles may exceed 40 miles in width. This beam width may force unwanted uplink visibility to dozens of towers spaced at 6 to 12 miles apart within a 2-D beam projection. Each additional tower within radio range may be subject to this interference and further amplify the problem.
During a transmission from an airborne source, this unwanted uplink visibility in the same RF frequency band may reduce network capacity to other airborne and ground-based users operating in the same frequency band in the vicinity. Antenna coverage angle may be one of many causes of interference to ground-based wireless networks.
During connectivity with a wireless network, proximal frequency use by another with increased power or increased transmission coverage may cause interference. A user in the same frequency band may interfere with connectivity. Wireless providers may operate in resource blocks or chunks of spectrum. Operation within these blocks of spectrum may preclude deconfliction among separate users
Various options have been considered to minimize interference between an airborne radio and a ground radio. One option may include specially equipped air communication tower locations (i.e. 100 mile spacing). This distance based option may provide each such equipped tower with an ability for split service (air/ground) for improved signal to noise (S/N) and connectivity to the aircraft. However, interference/desensitization issues to the ground users would still be a problem since the airborne radio may continue to transmit over non-equipped towers. Without a limitation on transmit directivity, many dozens of towers on the ground may receive an interfering wireless signal.
Therefore, a novel approach may be necessary to positively deconflict signal transmissions between an airborne user of a ground-based wireless network and a ground user of the ground-based wireless network. Through accurate and dynamic allocation of time slices of ground-based cellular bandwidth for use by an airborne user, and through downlink power control and frequency separation between air and ground uplinks, airborne users may achieve effective connectivity with a ground-based cellular network free from interference to connected ground users.